CIRCULATION. 



169 



third spinal nerve, through the ramus communicans of this nerve, into the 

 third sympathetic ganglion, up the sympathetic chain to the ganglion of the 

 vagus, and down the vagus trunk to the heart. 



Stimulation of Augrnentor Nerves. — The most obvious effect of the stim- 

 ulation of the augrnentor nerves is an increase of from 7 to 70 per cent, in the 

 frequency of the heart-beat (see Fig. 34). The quicker the heart is beating 

 before the stimulation, the less marked is the acceleration. The absolute maxi- 



Fig. 34.— Curve of blood-pressure in the cat, recorded by a mercury manometer, showing the 

 increase in frequency of heart-beat from excitation of the augrnentor nerves. The curve reads from 

 right to left. The augrnentor nerves were excited during thirty seconds, between the two stars. The 

 number of beats per ten seconds rose from 24 to 33 (Boehm, 1875, p. 258). 



mum of frequency is, however, independent of the frequency before stimulation. 

 The maximum of acceleration is largely independent of the duration of stimula- 

 tion. The duration of stimulation and the duration of acceleration are not 

 related, a long stimulation causing no greater acceleration than a short one. 



The force of the ventricular beat is increased. The ventricle is filled more 

 completely by the auricles, the volume of the ventricle being increased. The 



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Fig. 35.— Increase in the force of the ventricular contraction (curve of pressure in right ventricle) from 

 stimulation of augrnentor fibres. There is little or no change in frequency (Franck, 1890, p. 819). 



output of the heart is raised. There is no definite relation between the in- 

 crease of contraction volume or force of contraction and the increase in fre- 

 quency (see Fig. 35). Either may appear without the other, though this is 

 rare. The simultaneous stimulation of the nerves of both sides does not 

 give a greater maximum frequency than the stimulation of one nerve 

 alone. 



The strength and the volume of the auricular contractions are also in- 

 creased. The increase in volume is not due to a rise of pressure in the veins 

 — in fact, the pressure falls in the veins — but to a change in the elasticity of 

 the relaxed auricle, a lowering of its tonus. This change is not related to the 

 increase in the force of the auricular contractions that stimulation of the aug- 

 rnentor nerves also causes. It varies much in amount and i- less constantly 

 met with than the change in force. The changes in the ventricle and auricle 



